The invention relates to a steering wheel having a latching element for latching an airbag module to the steering wheel body and an electric contact.
Airbag units serve to protect a motor-vehicle occupant and these days usually form part of the standard equipment of a motor vehicle. Since installation of the airbag unit via screws has proven very complicated, various options for fastening it via latching connections have been proposed.
DE 296 02 630 describes a latching device for fastening an airbag module to a vehicle part, the latching device being designed in such a manner that pressing-on and/or rotating the airbag module causes a locking body to engage in a correspondingly shaped mating piece and the airbag module is thus fixed on the vehicle part. As the locking body, one exemplary embodiment provides a bent piece of spring steel which is wound around a cylindrical projection and can snap into a hook on a steering wheel body.
DE 296 21 295 discloses a device for fastening an airbag module in the steering wheel with at least one passive latching element and a pivotable or displaceable, rigid component as the active latching element, one element of which is provided on the steering wheel and the other element of which is provided on the airbag module. A resiliently mounted, pivotable hook is also suitable as the active latching element.
DE 195 08 816 describes an arrangement for fastening an airbag module to a steering wheel body, in which the mounting takes place by means of a bolt engaging in a resilient latch. In one embodiment, hooks are provided on the airbag module and leg springs on the steering wheel, the hooks being latched to a leg of the spring.
DE 197 25 684 discloses a steering wheel having an airbag module which is fastened to the steering wheel body by means of a latching connection, the latching connection having a resilient element which is tensioned during the installation process and snaps back into the fixing position when the latching takes place. This element is formed on the steering wheel or the airbag unit by a pretensioned wire ring which is secured to hook-shaped formations. Formations which push away the wire ring counter to its pretensioning during the installation and become hooked on the wire ring in the fixing position are provided on the airbag unit and on the steering wheel.
U.S. Pat. No. 5,350,190 describes connecting elements between an airbag module and a steering wheel, which elements enable the airbag module to move toward the steering wheel and away from the steering wheel. The connecting elements consist in each case of two parts, the first part being connected to the steering wheel and the second to the airbag module. The two parts engage telescopically in one another, are secured against slipping apart by an annular lip and can be latched in one another by this lip. The two parts are pretensioned with respect to each other, for example by a spring. These types of fastening do ensure simplified installation of the airbag unit. However, the arrangement of the airbag unit in the center of a steering wheel conceals a further problem. This is because usually the horn signal, which is intended to enable the driver to issue a warning signal in critical situations, is triggered by the pressure on the center of the steering wheel of the vehicle. In this case, at least a subregion of a covering is moved in the direction of the steering wheel body and an electric switching contact is therefore short-circuited.
U.S. Pat. No. 5,350,190 describes connecting elements between an airbag module and a steering wheel, which elements enable the airbag module to move toward the steering wheel and away from the steering wheel. The connecting elements consist in each case of two parts, the first part being connected to the steering wheel and the second to the airbag module. The two parts engage telescopically in one another, are secured against slipping apart by an annular lip and can be latched in one another by this lip. The two parts are pretensioned with respect to each other, for example by a spring. These types of fastening do ensure simplified installation of the airbag unit. However, the arrangement of the airbag unit in the center of a steering wheel conceals a further problem, because usually the horn signal, which is intended to enable the driver to issue a warning signal in critical situations, is triggered by the pressure on the center of the steering wheel of the vehicle. As a result, at least a subregion of a covering is moved in the direction of the steering wheel body and an electric switching contact is therefore short-circuited.
The arrangement of airbag units in the steering wheel causes problems with regard to the spatial arrangement of the contacts for triggering the horn. Although separate actuating levers, for example combined with switching levers for the light or windshield wipers, are used at discrete locations, they have proven disadvantageous, since the driver is not used to this and therefore requires an excessive amount of time in order to trigger the horn signal.
One attempt to solve this problem involves the xe2x80x9cfloating hornxe2x80x9d principle. In this case, the airbag unit is arranged on the steering wheel in such a manner that a pressure exerted by the driver on the airbag unit causes the horn signal to be triggered. Usually in this case, one contact is arranged on the airbag unit and one on the steering wheel and the airbag unit is connected to the steering wheel via flexible components. As a result, when a pressure is exerted on the airbag unit, movement of the airbag unit toward the steering wheel causes the contacts to be short-circuited and the horn to therefore be triggered.
Usually, the (electrically conductive) steering wheel frame or the generator support of the airbag unit form a first contact, and a corresponding, second contact is provided on the respective other part. In many cases, an additional contact bridge is arranged as the contact on the steering wheel.
In all of the above-described devices for latching an airbag unit to a steering wheel, additional parts have to be provided if the airbag unit is to be used according to the xe2x80x9cfloating hornxe2x80x9d principle for triggering the horn.
It is therefore desirable, in the case of an airbag fastening according to the xe2x80x9cfloating hornxe2x80x9d principle, to further reduce the number of required parts and, in the process, to make it possible at the same time to secure the airbag unit to the steering wheel body in a manner which is simple, secure and can be carried out without a tool.
This object is achieved by provision of a steering wheel having a latching element for latching an airbag module to the steering wheel body and an electric contact.
According to an embodiment of the present invention a steering wheel having a steering wheel body, an airbag unit, a latching connection for securing the airbag unit to the steering wheel body, and a contact device is provided. That contact device may include at least one first and one second contact which, in order to trigger an electric functional element, in particular an electric horn, are short-circuited if the airbag unit is moved in the direction of the steering wheel body by a pressure exerted on said airbag unit. The first contact may be a component of a latching element of the latching connection, and the latching element may be formed by a wire element.
For this purpose, the wire element of the latching connection is at least partially electrically conductive and at the same time forms a first contact of the contact device.
In this embodiment, the airbag unit is preferably secured to the steering wheel frame of part of the steering wheel body. However, in general steering wheel body is understood to mean the entire steering wheel without an airbag unit.
It is preferred for at least one elastic spacer element for setting a distance between the steering wheel body and the airbag unit to be provided. The spacer element can be deformed by a pressure being exerted on the airbag unit, as a result of which the first and the second contact are short-circuited. It is possible for the functions of the latching element and of the spacer element to be implemented in one component, for example in which the latching element is pretensioned and this distance between the airbag unit and steering wheel is also set in this manner and the movement of the airbag unit toward the steering wheel is made possible. However, separate elements are preferably provided, in which case the spacer element can at the same time secure the latching connection by counteracting any movement of the airbag unit toward the steering wheel which goes beyond the position designated for the inoperative position.
The second contact is preferably formed by at least one contact rivet. By latching element functioning as a contact, a further component is not required for the contact. The close, functional relationship between the latching element and the contact also simplifies the production by a separate positioning of fastening elements and electric contacts being rendered unnecessary.
In a preferred embodiment, the wire element extends essentially along the circumference of the airbag unit. The wire element can be secured either to the airbag unit or to the steering wheel.
The wire element is preferably embedded in the airbag unit or the steering wheel frame. In order to form the first contact of the latching element, a cutout is provided in the airbag unit or in the steering wheel frame and the latching element is accessible through said cutout and can be short-circuited by the second contact. By means of the embedding, the wire element is fixed in the airbag unit or the steering wheel frame and a displacement in the contact connection is effectively prevented even when relatively thin and elastic wire elements which are particularly suitable for the latching are used. Embedding in the airbag unit is possible in a particularly simple manner if, for example, part of the housing of the airbag unit or the generator support consists of plastic. The wire element can then be placed into the injection mold, when producing this part by injection molding, and injected during the production of the injection molded part.
As an alternative, it is also possible to latch the wire element to the airbag unit or to the steering wheel.
It is preferred for a piece of spring steel, preferably with a diameter in the range of from 1 to 5 mm, to be used as the wire element. The piece of spring steel firstly ensures the flexibility which is desired for the latching, and secondly has the conductivity required for the function as a contact. The use of wire made of other metals and alloys having suitable material properties is also possible.
The latching of the steering wheel and airbag unit preferably takes place by the wire element which is secured to one of the two parts having bow-shaped sections. The bow shaped parts are assigned to hook-shaped latching elements on the other part. The airbag unit is plugged onto the steering wheel and, when pressure is applied counter to the force exerted by the spacer elements, the bow-shaped sections are deflected from their normal position, with the result that they can slide past the hook-shaped latching elements. On reaching the fixing position, the bow-shaped sections snap into the assigned, hook-shaped latching elements and are then again situated in their normal position. As mentioned above, the bow-shaped sections and hook-shaped latching elements may be placed on either of the steering wheel or airbag units.
The spacer elements provided between the airbag unit and the steering wheel and the deflection of the bow-shaped sections, which deflection is required for latching purposes, prevent the latching connection from being able to be released by any further movement of the airbag unit and steering wheel toward each other. If necessary, the connection may nevertheless be released in a very simple manner by deflecting the bow-shaped sections using a suitable tool, such as a screwdriver.
Two and, in particular, three bow-shaped sections having assigned, hook-shaped latching elements are preferably provided. The use of three latching elements in an arrangement with respect to each other at suitable angles permits self-centering of the airbag unit. As a result, the contact gap can be kept particularly small, which is desirable both for esthetic reasons and also to provide a reduced risk of soiling.
In a particularly preferred embodiment, the wire element secured to the airbag unit and to the steering wheel is of annular design. It preferably has bows which extend essentially perpendicular with respect to the plane clamped by the wire element, from the airbag unit in the direction of the steering wheel and from the steering wheel in the direction of the airbag unit.
The hook-shaped latching elements expediently have a bevel on which the bow-shaped sections of the wire element are guided for deflection purposes during the latching of the airbag unit to the steering wheel. For example, a ramp can be provided. The lower surface of the hook can also have different forms. It is thus possible, for example, for the lower surface to be smooth, bevelled or curved.
Since according to the invention the wire element at the same time forms one of the contacts for triggering the horn, it is necessary to insulate the wire element from the second contact. A contact rivet is generally provided as the second contact. Depending on the design, the second contact can preferably be formed by a component of the airbag unit, for example the gas generator or the support thereof, or by the steering wheel frame. The component having the second contact is usually made of metal and is therefore electrically conductive. However, it is just as readily possible to connect the contact rivet via a cable.
If the latching element forming the contact is provided on the steering wheel, the bottom of a housing of the airbag unit, the generator support or the gas generator whose housing is usually metallic, expediently serves as a second contact. If the latching element forming the contact is provided on the airbag unit, the second contact is generally formed by the steering wheel frame which is in any case metallic.
The invention does not require the provision of an additional contact bridge.
In order to insulate the latching element forming the contact from the second contact, the latter is insulated in the regions in which it bears in the inoperative position against the part forming the mating contact. In the case of the preferred use of a wire element as the contact, plastic bushings in the form of clip elements, shrinkable tubing elements or a coating of dipping paint, for example, are suitable for the insulation. The latching element forming the contact can preferably be connected electrically via a connector lug.
The use of plastic bushings or a shrinkable tubing as insulating elements has the advantage that these act at the same time as damping elements for possible actuating noises.
The spacer elements ensure, on the one hand, that the airbag unit is securely latched to the steering wheel. On the other hand, they serve for setting the required distance, i.e. the contact gap, between the airbag unit and steering wheel in the inoperative position. The force which the spacer elements to oppose the movement of the airbag unit toward the steering wheel is determined to ensure hat the counterforce required for triggering the horn is not excessively great but large enough so that the horn signal will not be inadvertently triggered by vibration of unintentional touching. Helical springs are preferably provided as the spacer elements. Plastic parts having an appropriate elasticity are also suitable.
In order to secure the airbag unit from being displaced laterally with respect to the steering wheel, centering elements are preferably provided. Pins on one of the parts, which engage in corresponding depressions on the other part, are particularly suitable for this. In a preferred embodiment, the pins are arranged as centering elements within the helical springs serving as the spacer elements.